The invention is concerned with a bone compression plate. Such artificial bone compression or pressure plates used in osteosynthesis have either round holes formed with a spherical seat corresponding to the ball head of a screw or holes shaped like slits, which extend longitudinally along the plate and make a sliding movement of the plate possible. Screw holes which are countersunk for bone screws have been known for a long time and are used to ensure an osseous contact in the fracture area under compression. For the initial generation of pressure, that is, to press the two pieces of bone of the fracture together, a special clamping device, which is applied to the compression plate from the outside is used. This clamping plate is removed after the compression plate in contact with the pieces of fractured bone, has been screwed tight. In another embodiment, compression plates, in accordance with Swiss Pat. No. 462 375, are used. In this case, the countersunk holes (which correspond to the ball head of the screw as a horizontal half-cylinder and constitutes the seat for the screw) are provided in every sliding slit at the end of the slit, which is opposite the fracture. Chamfering is formed in the slit by a beveled half-cylinder which is inclined in such a way that when the screw head is sunk at that end of the sliding slit, the plate is, of necessity, pushed away from the location of the fracture in the longitudinal direction. If the plate is fastened by screws to the second of the two pieces of bone which are separated by the fracture, a longitudinal pushing of the fragment of the fracture, and consequently an automatic pressing of the two pieces of fractured bone against each other results from this longitudinal pushing of the plate. For the purpose of fastening the plate to the fractured bone, screws are sunk in a so-called neutral position in other slit-shaped holes in the plate to prevent a pulling apart of the fracture, that is, they are sunk at the place in the slit-shaped hole where the said inclined and horizontal half-cylinders run together.
In practice, both compression plates having round holes and those with slit-shaped holes, particularly those formed with chamfering to obtain the self-tightening effect which has been described above, are used. Depending upon the nature of the fracture, the surgeon will normally prefer a round-hole fastening having the advantage of a rigid connection between the screw, the bone and the plate and little necessary pressure of the plate on the bone. In other cases, he will use a sliding-slit fastening having the advantage of an automatic compression and the avoidance of any interference with the closing of the gap of the fracture. This choice will accept either the disadvantage of an interference effect in the case of round-hole fastening and a discontinuation of the compression, or even a pulling apart if the screw is placed eccentrically in the hole in the plate, in contrast with the disadvantage of a pulling apart in the case of a sliding-slit fastening if the screw is not placed precisely in the neutral position which could result in a loosening of the screw in the course of time.
To be able to use either screw holes of round or slit-shaped design, as desired, for optimum immobilization of the area of the fracture, compression plates of both kinds must therefore be available. Aside from the increased expense connected with this method, the application of the compression plate is unnecessarily made more difficult in many cases if the surgeon can only decide the most advantageous configuration of holes at the time of the insertion of the screws or, respectively, the pre-drilling of the bone part after bending the plate conformingly.
Making some of the screw holes in the compression plate slitlike in shape and others round, so that the compression plate is immovably fastened to the pieces of fractured bone after the final process of screwing the countersunk bone screws into the round holes is, in fact, known from Swiss Pat. No. 515 032. However, such compression plates incur the disadvantage that they are not universally usable any more because, depending upon the nature of the pieces of bone and the fracture, the slitlike holes and likewise the round holes have to be located at different places along the compression plate.
It is the object of the present invention to provide a compression plate of the type mentioned above, which contains exclusively slit-like holes for the corresponding countersunk ball-headed bone screws, but which makes possible an immovable fixing of the plate in the manner of screws of the round-hole type.
As explained below by means of exemplary embodiments of the present invention, with the aid of the drawings, the compression plate, according to the present invention, combines the advantages of plates with round as well as slit-like holes, avoids their disadvantages to a large degree and, additionally, has the important advantage of universal application with the possibility of being manufactured in a single model with no additional cost, with the exception that differing dimensions in length and width of the plate, necessarily and obviously, will be required.